The ubiquitous and ever-increasing occurrence of bacterial extrachromosomal elements or plasmids which confer antibiotic resistance, enhance pathogenicity or invasiveness, expand physiological capabilities or host range, specify bacteriocin production and/or confer conjugal donor ability is curtailing the effective prevention, diagnosis and treatment of bacterial disease. The work proposed herein is aimed at gathering fundamental information relative to plasmid occurrence and function in the cariogenic organism Streptococcus mutans. Within this context, the hypothesis that insoluble glucan synthesis is plasmid specified will be tested. Such glucans are thought to play a critical role in S. mutans-mediated caries formation by providing a matrix which facilitates colonization of the tooth surface by this organism. Strains representing the four genetic groups of S. mutans will be examined in this project. First, the genetic stability of glucan synthesis will be comparatively examined. Second, a variety of agents which promote the loss of plasmids will be examined for their ability to eliminate selectively glucan production in S. mutans. Third, representative strains of S. mutans and their glucan-deficient derivatives will be examined for the presence of covalently closed circular DNA. Such plasmid DNA will be characterized with respect to molecular weight, buoyant density, base composition and number of molecules per chromosomal equivalent. Furthermore, attempts will be made to correlate the presence of plasmid DNA with bacteriophage or bacteriocin production. The proposed research is expected to contribute fundamental information concerning plasmid occurrence, structure and function in organisms indigenous to the oral cavity. This work will have implications within the context of the control of bacterial-mediated caries formation, periodontal disease, and microbial colonization of the mouth. BIBLIOGRAPHIC REFERENCES: Macrina, F. L., G. G. Weatherly and R. Curtiss. 1974. R6K Plasmid replication: Influence of chromosomal genotype in a minicell-producing strain of E. coli. J. Bacteriol. 120, 1387-1400. Curtiss, R., F. L. Macrina and J. O. Falkinham. 1974. Escherichia coli - An Overview. In Handbook of Genetics, Vol. I, R. C. King, Editor. Plenum Press, New York.